The invention relates to the field of dispensing and, in particular, to dispensing systems that have a pair of intermediate filtering tanks that provide a filtering means for the liquid as it makes its way to a final destination, which may be e.g. domestic usage, pool water, etc. In such systems each tank acts as a separate filter so that one of the tanks may be periodically removed from the system without having to interrupt the supply of water as the other tank is used in its place.
Periodically, particles tend to build up on the filter which necessitates that the filter be backwashed (i.e. normal flow through the filter be reversed) in order to clean the filter. It is such a step that the applicant's invention provides on an automatic basis and also on an as-needed basis when used with an external differential pressure sensor. Periodically, it may also be necessary to cut off the flow entirely from one of the tanks in order to disconnect that tank for repair, replacement, etc. In that situation, the flow through the passages may be diverted in order to direct flow entirely through the other tank and not to the one being repaired.